1. Field of the Invention
This invention relates to secondary oil recovery systems and is particularly directed to apparatus for generating steam in a borehole to enhance oil recovery from adjacent formations and to drive a turbopump for delivering the recovered oil to the surface of the earth.
2. Description of the Prior Art
The use of steam for enhancing secondary oil recovery began in the United States around 1960. Originally, the process called for a steam generator located at the surface with the steam being injected into the treated well. Over the next twenty years, steam stimulation has gained wide acceptance and downhole steam generators have been developed, which are lowered into the borehole to generate steam in situ. Typical of these downhole steam generators is that disclosed in the copending application of William R. Wagner et al, Ser. No. 202,990, filed Nov. 3, 1980, assigned to the present assignee.
The Wagner device is a vast improvement over previous steam generators. However, there has still been considerable room for further improvement. With the steam generators of the Wagner type, the generator is lowered down the borehole to the level of the formation to be treated, where it generates steam and injects the steam into the formation. After a desired period of time, the steam generator is withdrawn from the borehole and is replaced by a pump which serves to produce the oil which was released by the steam. Obviously, a substantial period of time is required to accomplish this transfer and the steam-treated formation will be cooling down during this period. Consequently, much of the effect of the steam treatment is wasted. Moreover, the operations involved in lowering the steam generator into the borehole, subsequently removing it, and lowering the pump, require much labor and downtime, which add substantially to the cost of the process.